1. Field of the Invention
This invention relates to an evaporator, especially to an evaporator for a cooling system of an automobile.
2. Description of the Related Art
In order to improve the ability of a heat exchanger in general, a coolant is routed into or through several small tubes so that a larger effective heat exchange surface of the tubes can be provided and the distance between the coolant and the wall of a tube, through which the coolant flows, is decreased. An evaporator for a cooling system, a heat exchanger, has 8-10 divisional flows to achieve the above effect. An increase in divisions of the flow, however, creates turbulence, i.e. sections of the heat exchanger where coolant does not flow smoothly. This results in bad heat distribution as a whole. Japanese Patent Laid-Open 62-119373 (1987) discloses an evaporator with a junction which divides a coolant flow into two flows before the coolant goes into the evaporator. This doubles the number of flow paths as a whole without increasing the number of flows inside the evaporator and helps to prevent coolant flows from creating turbulence. As shown in FIGS. 1 and 9 of the above publication, a junction tube 6 has two branch tubes 3A, 4A which are connected to the evaporator. The end of each branch tube has a block 3A, 4A having a punched hole d. A bent portion a is formed at the periphery of the inlet opening 10 of the evaporator body. The branch tubes are set at the bent portions of the evaporator body. The parts of the evaporator are fixedly connected to each other by brazing. However, the junction tube divides the flow at a point in front of the evaporator body, the junction tube being relatively long. The inlet and outlet tubes extend across the core of the evaporator which causes an interruption or disturbance of the air flow. Replacement of the tubes outside of the core area is a problem because of the limitation in size when used in an automobile. Further, when the tubes are brazed after the evaporator is assembled, an additional process is required and even when the tubes are brazed in the same process as assembly of the evaporator, it is difficult to braze the tubes at the right place firmly, because the tubes are long and heavy. When using welding processes to fix the tubes to the blocks, which are brazed to the evaporator body, the corrugated fins near the tubes might melt.
Japanese Patent Laid-Open Nos. 52-37255 (1977) and 62-46195 (1987) disclose an evaporator which has a coolant inlet port and outlet port at its sides. This prevents a disturbing air flow, but mechanical strength may be a problem. As shown in FIG. 3 of Japanese Patent Laid-Open 52-37255 (1977), the end of the tube is supported by brazing only at the contact portion of the end of the tube and the bend of the plate. This type of structure may not provide enough strength. FIGS. 4 to 7 of Japanese Patent Laid-Open 62-46195 discloses different ways of providing support, but the tube is supported by only one contact point to the body.